Integrity testing of storage tank structure using robotic ultrasound

ABSTRACT

An objective of this invention is to provided apparatus and methods to test the integrity of empty and full tanks. Another object of this invention is to provide a granular inspection of the tank. Another object of this invention is to provide precision positioning information of sample points. Another object of this invention is to provide automated inspection pattern and correction. Another object of this invention is to minimize hazardous working conditions.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application takes priority to provisional application No.62/122,911 filed on Nov. 3, 2014 and incorporated herein, in itsentirety, by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable

INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC

Not Applicable

BACKGROUND

Storage tanks must be inspected periodically to determine whether a tankis in need of replacement or repair. Inspections detect corrosion,fissures, cracks, and other anomalies in tank walls and floors.Inspection techniques may include acoustic, electrical and/or mechanicaltechniques. Inspection reports usually contain basic measurements and anestimate of metal loss.

Tanks must be empty for inspection because testing personnel must haveaccess to the inside of the tank. Consequently, inspecting fluid filledtank walls becomes expensive and dangerous. In most cases, tankoperations in at least two tanks must stop so that fluid from the tankto be inspected can be pumped into a holding tank. The tank to beinspected may have to be cleaned before inspection personnel can enterthe tank. Inspection personnel will, more likely than not, be requiredto wear personal protection equipment and carry oxygen to inspect tanks.Once inspection is completed, fluid must be pumped from the holding tankinto the inspected tank.

FIG. 1 shows a typical tank used by refineries, storage facilities, andpipelines. Other tanks include, but are not limited to, tanks on supertankers, off shore oil production platforms, Floating Production Storageand Offloading vessels (FPSOs), airport storage tanks and oil-transportrail cars. Volatile petroleum products that may be stored in these typesof tanks include flammable and combustible liquids and gases, and mayproduce flammable or combustible liquids, gases, vapors or mists whenmixed with air under normal atmospheric conditions. The normal operatingtemperature range for this type of system is −20 C to +60 C at normalatmospheric pressures of 980 to 1050 millibars. Taking a typical tankout of operation, cleaning, and inspecting it can cost in theneighborhood of $5,000,000.

SUMMARY OF THE INVENTION

An objective of this invention is to provide an apparatus and method totest the integrity of empty and full tanks. Another object of thisinvention is to provide a granular inspection of the tank. Anotherobject of this invention is to provide precision positioning informationof sample points. Another object of this invention is to provideautomated inspection pattern and correction. Another object of thisinvention is to minimize hazardous working conditions.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the present invention will becomeapparent in the following detailed descriptions of the preferredembodiment with reference to the accompanying drawings, of which:

FIG. 1 is an environmental view of an exemplary tank;

FIG. 2 is a perspective view of the ROV;

FIG. 3 is a bottom view of the ROV;

FIG. 4 is a top view of the ROV;

FIG. 5 is a sectional view of the ROV taken from A-A;

FIG. 6 is a schematic showing safe area operations;

FIG. 6a is a side perspective view of an exemplary hydrophone basestation;

FIG. 7 is a schematic showing an exemplary safety interlock system;

FIG. 8 is multi-beam type phased array schematic;

FIG. 9a is an exemplary schematic of an exemplary tank floor plan;

FIG. 9b is an exemplary schematic of ROV positioning;

FIG. 9c is an exemplary schematic of ROV positioning superimposed on atank floor plan;

FIG. 9d is an exemplary schematic showing data from the multi-beamphased array;

FIG. 9e is an exemplary schematic of survey data superimposed on a tankfloor map;

FIG. 9f is an exemplary schematic of a survey data superimposed on atank floor map;

FIG. 9g is an exemplary completed survey map.

DETAILED DESCRIPTION OF THE INVENTION

In the following detailed description, reference is made to theaccompanying drawings, which form a part hereof. In the drawings, theuse of similar or the same symbols in different drawings typicallyindicates similar or identical items, unless context dictates otherwise.

The illustrative embodiments described in the detailed description,drawings, and claims are not meant to be limiting. Other embodiments maybe utilized, and other changes may be made, without departing from thespirit or scope of the subject matter presented here.

One skilled in the art will recognize that the herein describedcomponents (e.g., operations), devices, objects, and the discussionaccompanying them are used as examples for the sake of conceptualclarity and that various configuration modifications are contemplated.Consequently, as used herein, the specific exemplars set forth and theaccompanying discussion are intended to be representative of their moregeneral classes. In general, use of any specific exemplar is intended tobe representative of its class, and the non-inclusion of specificcomponents (e.g., operations), devices, and objects should not be takenas limiting.

The present application may use formal outline headings for clarity ofpresentation. However, it is to be understood that the outline headingsare for presentation purposes, and that different types of subjectmatter may be discussed throughout the application (e.g.,device(s)/structure(s) may be described under process(es)/operationsheading(s) and/or process(es)/operations may be discussed understructure(s)/process(es) headings; and/or descriptions of single topicsmay span two or more topic headings). Hence, the use of the formaloutline headings is not intended to be in any way limiting.

Referring to FIGS. 2-6, embodiments are provide for an automated tanksurveyor (“ROV”) (100) that mobilizes at least an ultrasound measurementsystem (200) and an acoustic tracking system (401) to survey tank wallsand floor to detect corrosion, fissures, cracks, and other anomalies.The ROV (100), the ultrasound measurement system (200), and the acoustictracking system (401) receive and transmit data to a telemetry system(105). The telemetry system (105) is any known automated communicationsprocess by which data is received and transmitted. The telemetry system(105) is positioned at a location outside a tank (10). In someembodiments the ROV (100) is further comprised of a plow (300) which maybe used to displace sediment that may occlude sound path between theultrasound measurement system (200) and the surface to be measured.

In some embodiments, the ROV (100) has six traditional underwaterthrusters (101) used to generate five degrees of freedom motive forcewhen swimming: surge (forward/reverse), sway (port/starboard), heave(vertical), roll (CW/CCW), and yaw (turn port or starboard). The ROV(100) moves in “flight mode” through liquid to a particular area of thetank to be surveyed, and then transitions into “crawler mode” forprecise surface positioning using continuous tracks (102) and at leastone vortex generator (103) (described in U.S. Pat. No. 6,881,025). Thismobility system allows the ROV (100) to remain motionless, to crawlalong vertical tank walls, or plow through sludge, for example. The ROV(100) is powered and controlled through an electronic communicationscable (411) connected to a telemetry system (105).

In some embodiments, the ROV is further comprised of obstacle avoidancesonar (400). The obstacle avoidance sonar (400) may be passive or activeand communicates with the telemetry system (105).

The acoustic tracking system (401) helps the ROV (100) avoid obstaclesand navigate within the tank. The acoustic tracking system (401) iscomprised of at least one pinger (403) and at least three hydrophonebase stations (402) operably attached to the outside of a vessel (10)wall; preferably, the hydrophone base station (402) magneticallyattaches. Preferably, the acoustic tracking system (401) is comprised ofat least four hydrophone bases stations (402 a, 402 b, 402 c, 402 d).Preferably, the four hydrophone base stations (402 a, 402 b, 402 c, 402d) are mounted on the North, East, South, and West sides of a tank atvarying heights. To alleviate potential problems due to acousticshielding by structures inside of the tank (e.g. ladders and pipes) morethan four hydrophone base stations (402) may be used.

The pinger (403) and the hydrophone base station (402) have a commonclock. Preferably, the clock has μs accuracy. To mark the location ofthe ROV (100) a simultaneous electronic timing pulse goes out to thepinger (403), signaling it to send out a pulse, and the hydrophone basestations (402), signaling each hydrophone base station (402) to startits clocks. As each hydrophone base station (402) receives a pulse fromthe pinger (403), the common clock is stopped. The ‘time of flight’ datafrom each hydrophone base station is passed to the telemetry system(105) where the data may be passed through any known triangulationalgorithm in order to accurately locate the ROV (100).

Referring to FIG. 7, in some embodiments, the ROV (100) has a safetyinterlock (410). The ROV (100) may be powered by high voltage. Becausethe ROV (100) must be able to move in liquid it cannot be made explosionproof or it would be too heavy to “swim”. However, once the ROV (100) isbelow the surface of the liquid in a tank, it is no longer in ahazardous area. A safety lock (410) is used to ensure that the ROV (100)is never under power when in transition through hazardous areas. The ROV(100) can be powered up only when it is located a safe distance belowthe surface of the liquid in the tank.

The safety interlock (410) is comprised of two independent systems: anintrinsically safe pressure transmitter (430) and the acoustic trackingsystem (401). The intrinsically safe pressure transmitter (430) willcontinuously measure the ambient pressure at the top of the ROV (100);as the pressure increases the depth of the ROV (100) increases in thetank. The intrinsically safe pressure transmitter (430) measures the sumof the weight of the fluid column and the ambient atmospheric pressure;ambient pressure can vary greatly over time. Consequently, a barometricpressure transmitter (431), located in the safe area, will continuouslymonitor ambient atmospheric pressure. The difference between thebarometric pressure transmitter (431) and the intrinsically safepressure transmitter (430) can be used to more accurately measure thedepth of the ROV (100), confirming it is below the ROV exclusion zone.

Preferably, a custom EX rated umbilical cable (411) will connect fromthe telemetry system (105) in the safe area to the ROV (100). Inside theumbilical cable (411), a separated jacketed and screened twisted pair ofwires is used for the safety interlock (410). The remaining conductorsand optical fibers in the umbilical cable (411) provide a pathway forelectrical power, ROV (100) control and sensor data. Preferably, theumbilical cable (411) is jacketed with a material that is compatiblewith the fluids in the tank and flexible enough to allow the ROV (100)to have free movement. Preferably, the umbilical cable (411) isnegatively buoyant and will sink to the bottom of a tank filled withliquid.

To ensure the ROV (100) is safely isolated from the hazardous areaduring operation, an ROV exclusion zone (420) extends from the surfaceof the liquid in the tank down to a predetermined depth. The ROV (100)can only be powered up when it is in the fluid below the ROV exclusionzone (420). If during deployment or during operation, the ROV (100)approaches the ROV exclusion zone (420), the operator will be warnedwith at least and audible and/or visual alarm (421). If the ROV (100)enters the ROV exclusion zone (420), the system will be immediately andautomatically powered down, and distinctly different audio/visual alarms(442) will identify the reason for shut down.

Referring to FIGS. 1-6, 8, preferably, the ultrasound measurement system(200) is a multi-beam type phased array. The phased array ultrasoundmeasurement system (200) is comprised of a plurality of ultrasonictransducers, each of which can be pulsed independently. By varying thetiming of each transducer to pulse one by one along a row, a pattern ofconstructive interference results in a beam at a set angle. In otherwords, the beam can be steered electronically. Preferably, the beamprofile has less than 2 dB drop between transducers allowing a very highdensity of energy in the tank floor improving performance. The beam typephased array system (200) may be steered in pattern format to examinetank walls and floor. In some embodiments, depending on tank size orsuspected anomalies, more than one beam type phased array system (200)may be used.

Steering the beam typed phased array system (200) allows the tankinspector to utilize a defined search pattern so that anomalies ofvarying types are found and accurately defined. The search pattern ofthe ROV (100) is dependent on the characteristics of the environment tobe inspected. Exemplary search patterns include increasing concentriccircles, decreasing concentric circles, grid pattern, plate by plateamongst others regardless of the inspection pattern selected, the ROV(100) provides near continuous inspection of a tank. The frequency withwhich samples are taken is determined by ultrasound pulse repetitionfrequency and the speed of the ROV (100). Range resolution (Δr) is afunction of ultra sound frequency (f), the sound velocity in the mediabeing tested (cΔt) and the number of pulses (Δt):

Δr=cΔt/f*Δt/2.

The ROV (100) typically uses a single pulse for each transmit cycle, soΔt=1.

For example, assuming a single pulse at an ultra sound frequency of 6.2Mhz in water (1500 m/s), the range resolution would be 121 μm (0.0048″).Given a 10″ linear array, the lateral resolution would be similar, witha vertical resolution of half the lateral resolution.

Referring to FIGS. 9a-9g , the telemetry system (105) compiles the datareceived by the ultrasound measurement system (200) and the acoustictracking system (401) to measure anomalies in the tank. The telemetrysystem time-stamps, sample-frame by sample-frame, data collect in eachframe from the ultrasound measurement system (200) and the acoustictracking system (401). Correlating the timestamps of each set of dataprovides a direct, 3D position fix of where each ultrasound sample wastaken and whether anomalies were found. In one embodiment, a tank floormap (900) is loaded into the telemetry system (105) prior to survey of atank (10). The tank floor map (900) describes, at a minimum, tankidentification, tank location, tank size, position and original, asinstalled thickness of each floor plate, and any obstacles (e.g. sumps,pipes). The correlated data may be overlaid on an imported tank mapassembling a survey report.

What is claimed is:
 1. An apparatus to test the integrity of a vesselcomprising an automated tank surveyor mobilizing at least an ultrasoundmeasurement system and acoustic tracking system.
 2. The apparatus ofclaim 1 where the acoustic tracking system is comprised of at least onepinger and at least three hydrophone base stations; where the acoustictracking system tracks the location of the automated tank surveyor inthe vessel.
 3. The apparatus of claim 2 further comprises a safetyinterlock having at least two independent systems: a pressuretransmitters and the acoustic tracking system; where the pressuretransmitter continuously measures the ambient pressure at the top of avessel.
 4. The apparatus of claim 3 where the automated tank surveyor ispowered up only when it is below a pre-determined exclusion zone.
 5. Theapparatus of claim 3 where the automated tank surveyor is powered downwhen it is above a pre-determined exclusion zone.
 6. The apparatus ofclaim 1 where the automated tank surveyor is further comprised of asediment plow.
 7. The apparatus of claim 1 where the acoustic trackingsystem is comprised of at least one multi-beam phased array; where themulti-beam phase array is steered in a pre-determined pattern.
 8. Theapparatus of claim 7 is further comprised of a telemetry system thatreceives and compiles data from the ultrasound measurement system andthe acoustic tracking system.
 9. The apparatus of claim 8 where thetelemetry system is pre-loaded with a template of the interior of thevessel; where the template is divided into a plurality of sample frames;where the telemetry system time-stamps, sample-frame by sample-frame,data collect in each frame by the ultrasound measurement system and theacoustic tracking system; where the telemetry system correlates thetimestamps of each data set providing a direct, 3D position fix of whereeach ultrasound sample was taken.